Key Takeaways:
- The Martian polar vortex exhibits significantly lower temperatures (approximately 40°C colder) within its core compared to the surrounding atmosphere, a phenomenon observed through the use of the ExoMars Trace Gas Orbiter and Mars Reconnaissance Orbiter data.
- This extreme cold within the vortex leads to the accumulation of ozone due to the freezing out of water vapor, which typically destroys ozone through interactions with solar radiation.
- The study of ozone levels within the Martian polar vortex provides valuable insights into the planet's atmospheric chemistry and its evolution over time, including potential past presence of a protective ozone layer.
- Observations were challenging due to the polar night; data acquisition relied on detecting temperature drops to identify the vortex's boundaries and combining data from the Atmospheric Chemistry Suite (ACS) and the Mars Climate Sounder.
Planetary scientists studying Mars have discovered that its polar vortex has temperatures much lower than predicted. A polar vortex is a low-pressure system of air that rotates around a planet’s poles. Earth has such areas around both of its poles. They’re weaker during each hemisphere’s summer and stronger in winter.
As on Earth, Mars’s polar vortex forms because the planet tilts at an angle of 25.2°. Earth’s tilt is 23.5°. This inclination gives the Red Planet seasons. And like on Earth, at the end of its northern hemisphere summer, a polar vortex develops over Mars’s north pole.
Recently, researchers had a rare glimpse into the Red Planet’s north polar vortex. They discovered that temperatures inside it are far colder than outside, and that it causes a surge in ozone in the atmosphere.
“The atmosphere inside the polar vortex, from near the surface to about 30 kilometers high, is characterized by extreme cold temperatures, about 40 degrees Celsius colder than outside the vortex,” said Kevin Olsen of the University of Oxford in a statement. Olsen presented the results at the EPSC-DPS2025 Joint Meeting in Helsinki last week.
“Because winters at Mars’s north pole experience total darkness, like on Earth, they are very hard to study,” says Olsen. “By being able to measure the vortex and determine whether our observations are inside or outside of the dark vortex, we can really tell what is going on.”
When the atmosphere is that cold, ozone can accumulate in the vortex. Normally, this wouldn’t happen because water molecules destroy ozone as solar radiation break them down. But at the temperatures measured, all the water vapor in the atmosphere freezes out and falls onto the ice cap. No water vapor means the ozone can accumulate within the vortex.
Related: Mars water-ice clouds are key to odd thermal rhythm
“Ozone is a very important gas on Mars — it’s a very reactive form of oxygen and tells us how fast chemistry is happening in the atmosphere,” said Olsen. “By understanding how much ozone there is and how variable it is, we know more about how the atmosphere changed over time, and even whether Mars once had a protective ozone layer like on Earth.”
Technology to the rescue
Olsen and his team work with the European Space Agency’s ExoMars Trace Gas Orbiter that is in orbit around Mars. Normally the spacecraft’s Atmospheric Chemistry Suite (ACS) studies Mars’s atmosphere by looking through it toward the Sun. By analyzing that filtered sunlight, the team can see which wavelengths are absorbed. They then know which molecules are present and how high above the surface they are.
During the martian winter, there’s no sunlight over Mars’s north pole. But the team only could see inside the vortex when it loses its circular shape. For this, Olsen collected temperature data from the Mars Climate Sounder instrument on NASA’s Mars Reconnaissance Orbiter.
“We looked for a sudden drop in temperature — a sure sign of being inside the vortex,” said Olsen. “Comparing the ACS observations with the results from the Mars Climate Sounder shows clear differences in the atmosphere inside the vortex compared to outside. This is a fascinating opportunity to learn more about martian atmosphere chemistry and how conditions change during the polar night to allow ozone to build up.”
